Retarded electromagnet



July 29, 1952 L. R. RANsoN .RETARDED ELECTROMAGNET 3 Sheets-Sheet 1 Filed Nov. 9, 1945 P/uny er Tfno/Cc INVENTOR.

/oy d /fuss e// fama/1 #War/rf y July 29, 1952 L. R. RANsoN 2,605,327

RETARDED ELECTROMAGNET Filed Nov. 9, 1945 3 Sheets-Sheet 2 /ao ma a? atented .uly 29, 1952 STATES 2,605,327 ADE LECTMGNE'T Linfyiinsu nnsbn, shaker High't'si ohiuj, s-

signor to The Clark Controller C'o'nipay; Cleveland Ohio; a corporation of Ohio Aisliiitaiiii Navasa 9,1945', serial N. 627,735

The invention `relates to electro-'magnetically operated timing devices; and particnlarly to electiO-fna'gi'i'etic timing dei/'lees Wrliich 'awtnie nterval is introduced between the moment of energizing an electro-magneticwinding and the moment `at which the Amagnetism produced by the. winding performs a useful function of operation, A i .n

In general the; embodiment of, the invention comprises an' electro-magnetic' winding; and an air ygap of work gap tliroughwnich magnetism; or magnetic flux produced' bythe winding; acts to perform a' useful operation; and means `to cause themagneticfluxin the work gap to betoo weal; to perform the operation 'at the moment when' the Winding is' first energized and toA cause the strength ofthe lflux in thework gapI to grad-v ually increase tothe operating value' at a con'- trol'ljed' or timed rate. l

The invention is applicahleto numerous uses in various arts; but onewof itsinost important uses' or functions is to timeor delaytl/ i'e operatin of electromagnetically operated electric switches or contaeto'rs'; and for that reason it willbeillustrated and described herein as applied l '00 that 11S?! i o.. Y n is among the objects ofthe invention; To provide V,generally van;l improved timing'l and' operating deviceof the lclass; referred to above;

To provide generallyan improved electro-magnetically operated` apparatus timedl to operate 5' with delay in an improved manner;i H

To provide' an improved electro-magnetically actuated' apparatus in which an operation is magnetically performed after the relapse of a time interval following' energi'zation of an electromagnetic" Winding, by magnetic pull on a movablev element; and in which the magnetic pll increases at an' accelerating rate having imi proved characteristics as thev time interval goes' AOther objects will become apparent tor those skilled in the art t'o which the' invention appertains.

The invention is fully disclosed in the follow'- ing `description takenin connection with the accompanying drawing, inwhich;

lisa side elevational View partly broken away and in section of an i electric contactor, and showinglnvside elevation a timing and operating device embodying a part of my invention applied thereto; v v d y v y,

FigQZ is a View showing the ytiming and operating device off Fig. 1' in llongitudinal section, and to al larger scale than in Fig. 1', and with parts of Fig. 1 shown fragmentarily;

iiux is in two' parts: the initiai ida'd df stati'n aels'howing a hieietiohgi, Y. Fig. 4 is a view similar to'Fig. vlsliotvirig a medi"-y flcaiiom, l Fig? Sois a View to nliredlale' of@` P" ,91 Fig. 2 showing an adjustment which 'may beeinplevedor a valve device fi is i` diagrammatic view-i11sirai'meif tainy magnetodynamicpiq rties 'b'otli' of the invention and of Certain pr ai; i 4Figl- 71S @View eenrll'yir te," ,i I'iLSh ing another kind of valve device which li'y may employ; VVFig. 8 is a fragmentaryview showinga mtjdiiication whi'zli-HI` may employ of an attaching and secrin'g device of liligs..v l2, 4; or?, t

In the patent tp charles Riiipi, iss ed o ber 8, 1929, No. 1,730,688, is disclosed contacter provided witha delaying or tiniin operating device in the same generalclass or the present invention; and the presepi tionwhen applied to an e be considered as an improvementovero-`th closure' of that pateiit. Referring @et atpjaite the is" energized b develops in an"v air gap' or werk gapV between the contacter aim lsA andthe adjaefit iia f iii-agi netic plunger 35; enclosed in'y Aand able in sealed oil-containing chamber 2'8l Iliade of nonVI4 magnetic material..

The magnetic pun of this nur iii this gab tfno to move the contacter arm I6` to close the con: tacts 1'2-44; but is insumcientzio `do 'so/bee ofthe lengtl'r and reluctance of the long air gap and the consequentk weakness of the fluir.

This magnetic pull;` however," isA greatxenougl" tqfpullthe nlunger forwardly in' the chamber 28 against theoppcsingforce of a'spring liliana! it wmoves forwardly, its movement being retarded by, a now restrictinglvalvei arrangement; at the; rear of tlie plunger, through Whieh oi'lpdisplaeed il .ne

3 the arm IS to move against its bias; and the final lead of forcing the contacts l2-I4 together into pressure engagement at the end of the arm movement.

This contact engaging force must be sucient to enable the contacts to carry the desired current; and sucient to prevent the contacts from separating or vibrating one upon the other when they iirst engage with a blow or thereafter when the contacter as a whole is subjected to shocks, which vibration or separation, if it should occur, will draw momentary arcs at the contacts and weld them together.

This nal load, or, the minimum force necessary to firmly engage the contacts and hold them engaged, is a iixed or pre-imposed quantity for any given size of contacts, whereas the initial. load or force to start the arm I6 moving may be made large or small, and arbitrarily chosen,

by adjusting the gravity or other bias holding the arm in normal open-contact position.

Now it has been found that, with the arrangement of parts of the said patent, the magnetic pull on the arm I increases approximately rectilinearly with movement of the plunger that is to say. it varies approximately inversely proportionally with the length oi the air gap between the arm and the plunger.

A characteristic curve of pull for such prior art arrangement is shown by the curve A in Fig. 6; ordinates representing magnetic pull on the arm, and abscissae representing diierent positions of the plunger as it moves through its range of movement er stroke, that is, toward the left in Fig. 6.

The curve A has been made experimentally with the arm I6 of the patent held in fully retracted, biased position, the solid line curve A corresponding to the full stroke of the plunger from o to a.

When, as in practice, the arm I6 is held open by its bias alone and is free to move, it will start to move when the pulling force is at the point b on the curve A corresponding to the position o-c for'the plunger, at which the magnetic pull crosses the bias-load line d and overbalances the bias. Thereafter the arm I6 moves and the plunger 35 continues to move, and the working air gap is shortened by both movements going on concurrently; and, by the time the contacts are closed, the pull holding them closed will be at the point e, the pull from b to e rising along thedotted line j due to shortening of the'working air gap by arm movement.

From this pull curve A, it will be seen that in order to have at e sufficient magnetic pull and force to hold the contacts securely closed (for the purposes mentioned above) there will unavoidably be a relatively large magnetic pull at b when the arm I6 starts to move, because the pulls at e and b cannot be greatly different due to the rectilinear character of the pull curve; and to prevent the arm from moving prematurely, it must therefore be heavily biased in the open direction, with a bias equal to the force b, to hold it open until the timing interval of the moving plunger has run. The result is that for the sake of having ample contact engaging force, the bias of the arm I6 must be correspondingly great, and the winding must accordingly provide abnormally high ampere turns to move the arm, and the whole contacter must be of abnormally large proportions. Another Way to Say this is, that for a contacter, winding, etc. of given size and cost, there is a low limit to the force avail- 4 able to hold the contacts closed, and the current carrying rating of the contacts must be low. Satisfactory operation therefore is attained with a sacrifice of economy.

In order to overcome this economic disadvantage of the device of the patent a problem is presented.

According to the present invention this problem has been solved by causing the pull on the contacter arm to be relatively weak during the major part of the stroke of the plunger and while the arm is in the open-contact position; and to become abruptly stronger and rise rapidly to a high value near the end of the plunger movement, and near the end of its timed interval.

This enables the contacter arm to be held unmoved by any desired bias, er even small bias, and at the same time provides very great contact engaging force.

The present invention and the means by which this result is accomplished will new be described.

Referring to the drawing, I have shown in Fig. 1, a conventional electric contacter provided with an operating and timing device i, which constitutes part of my invention, applied thereto.

The contacter itself comprises a magnetic frame element 2, mounted upon an insulating panel 3, by any suitable number of screws or bolts 4, and having a forwardly projecting leg 5, upon which at 6 is pivoted a contacter arm 7, carrying at its upper end a contact 8, movable therewith, and engageable, upon movement of the arm, with a stationary contact 9, mounted upon a post I0, secured to the panel 3 by means of a stud Il, to which electric circuit connection can be made. The contacter arm 1 may be in two parts as illustrated, the contact 8 being mounted upon a supplemental arm i3 pivoted as at I5 to the main arm 1, in a well known manner, and for well known purposes.

The contact 8 is connected by a flexible cable il to a post I8, secured to the panel by a stud I9, to which electric circuit connection can be made.

The arm 'l and its contact 8 are normally biased by gravity to the open-contact position Shown, the arm having a. shoulder 2| resting upon a screw 22 in the leg 5, whereby the open position of the arm may be adjustably changed.

The arm 'l is preferably provided with a flat magnetic pole face 23.

The timing and operating device referred to hereinbefore is shown in elevation at l and will be more fully described in several forms, but in general it comprises a cylindrical structure 24 disposed in the hollow core of an electro-magnetic energizing winding 25 and having a flat magnetic pole face 25 opposite the pole face 23 of the arm 'i and spaced therefrom, providing thereby an external working air gap 21. Rearwardly of the winding 25 as at 29, the device is of reduced diameter and projects through aligned bores or holes in the panel 3 and in the magnetic frame element 2 respectively; and the reduced diameter provides a shoulder 30 engaging the frame element 2 to predeterminedly position the device as a whole longitudinally. The device is held in this position by a bracket 3| mounted upon the panel 3 by screws 32-32 and overlapping the rearward end of the reduced diameter portion 29, and by a screw 33 projected through the bracket and screwed into the device, and these parts are made so that the shoulder 33 is drawn rmly against the frame element 2.

Means ynot shown but well understood in the art is provided to hold the winding against the frame element l in a well known manner.

The operation of the device as a whole will be apparent. When the winding 25 is energized, magnetic flux is produced in the lair gap 211 between pole faces 23- and 26, tending to move the arm 1 clockwise, as viewed in the drawing, to engage the contacts 8 andg. At the time of energizing the winding the ux in the gap 21 is insufiicient to overcome the bias of the arm 1 to move it, Ibut after the passage of a time interval,

vdetermined by the timing device l in a manner to be described, the flux strength in the gap 21 increases suiilciently to move the arm 1 and engage the contacts; When the winding is deenerg'ized the bias of the arm 1 restores it to its normal position and disengages the cont-acts.

The interior construction and mode of operation of the timing and operating device l Will now be described and reference may be had first to the form of Fig. 2; wherein some of the parts of Fig. l have been reproduced fragmentarily.

A liquid-tight, ltubular chamber 34 is provided preferably cylindrical in cross section as'indicated in the drawing. The side wall comprises' generally a forward portion 36 of non-magnetic material such as brass, and a rearward portion 38 of magnetic material such as steel, the two parts being turned down so as to telescope one within the other at an airtight liquid tight juncture indicated at 39. IThe inside diameter of these two tubular portions is uniform. The outside diameter of the part 36 is somewhat greater than that of the part 38 to provide the aforesaid shoulder 30. At the juncture 39, the tubular part 38 may be cut back to provide a groove 40 which may be filled with solder 4I to seal the juncture. The rearward end of the tubular chamber is closed and sealed by a plug 42 of non-magnetic material such as brass, screw threaded into the end of the tubular wall 3B. The plug 42 has a flange 43 overlapping the end of the ,tubular wall, and the liquid tight seal effected by the end of the plug and the ange 43 may be further insured by a ring of solder 44 sealing the flange 43 and the end of the tube together.

The lug 42 has a threaded hole 45 therein into which the aforesaid screw 33 is screwed for positioning the device in connection with the bracket 3| as has already been described in connection with Fig. 1.

The forward end of the tubular wall 36 is sealed by a plug or pole piece 46 of magnetic material, screw threaded into the end of the tube as shown, and the juncture may be further sealed by providing a groove and iilling it with solder as at 41.

The pole piece 46 has the exterior transverse pole face 26 already described for Fig. l. The forward face of the winding 25 described for Fig. l is indicated diagrammatically by the broken line 25 in Fig. 2, from which it will be seen that the pole piece 46 projects forwardly out of the winding, and projects inwardly into the winding for a substantial distance. The inner end of the pole piece 46 has a transverse pole face 48 well within the winding.

The flat or planar pole face 26 extends transversely of the axis of the pole piece 46 substantially at right angles thereto; and the pole face 23 is substantially parallel to th pole face 26 and becomes parallel as it moves in operation; so that the air gap 21 between the faces 23 and 6 26 is of substantially uniform length in the direction of the flux coming axially out of the pole piece 45.

A plunger 49 is provided in the tubular chamber 34 and has a free-sliding piston-like fit therein. It has a longitudinal bore 5D and a shoulder 5l in the bore, and a coil compression spring 52 abuts at one end upon the shoulder 5|, and extends out of the bore and into engagement with the pole piece 46. Preferably the pole piece 46 has arecess or bore 53 therein to receive and center that end of the spring. The plunger 49 is thus spring-biased toward the rear of the chamber 34. The plunger at its forward end has a transverse pole face 54 parallel to the pole face 48; and thereby is provided a magnetic air gap 55 between the pole faces 48 and 54.

The bore 50 constitutes part of a passageway extending entirely through the plunger and at its rearward end this passageway is enlarged to provide a cavity 56 in the nature of a housing for a valve structure.

At the rearward end of the valve cavity 56 is a cylindrical outlet 51, see Fig, 5, which may be provided in any suitable manner. The means shown comprises a thim-ble 58, having a iiange 59, seated in an annular recess in the end of the plunger, the end of the plunger being peened over the iiange as at 60 to retain it in position.

A valve shown generally at 6|, is provided with a ange 62 normally resting upon a shoulder 63 at the forward end or bottom of the cavity 56 and normally retained thereon by a spring 64 abutting upon the valve iiange 62 and reacting upon the said flange 59. The valve iiange 62 has a transverse passageway or groove 65 therein, affording communication between the bore 50 in the plunger and the cavity 56. Rearwardly of the ange 62 the valve is provided with a slightly conical throttle portion 66 axially aligned with the cylindrical outlet 51, and guided to enter it by a flange G1 on the valve, disposed in the cylindrical outlet 451. To prevent the iiange 61 from obstructing the cylindrical outlet 51, it is preferably made circular to slidingly t the outlet and then ats are cut on its periphery as shown in the drawing.

In assembling the parts of Fig. 2, the pole piece 46 may be screwed into the chamber 34 and sealed therein as described. The valve parts may be assembled with the plunger 49, as a unit. A measured quantity of oil or other suitable liquid is put into the chamber.

The oil is not shown in cross section in Fig. 2 to avoid obscuring the parts of the structure, but is indicated by its level at 106 in the working air gap 55; and it is believed that this will make clear the presence of the oil in the gap 55, bore 56, cavity 56, etc. particularly in view of the aforesaid prior patent. The same indication of the oil has lbeen made in Figs, 3, 4, and 7 to be referred to. The spring 52 and the assembled plunger are then put into the chamber and the end plug 42 is screwed in and sealed as described.

The operation of the device of Fig. 2, and in connection with parts of Fig. 1 fragmentarily shown therein, is as follows. The plunger 49 is normally spring-biased to the rearof the chamber 34 by the spring 52, the end 60 abutting against the plug 42. When the winding 25 is energized with predetermined ampere-turns, for example by being connected across a source of potential, magnetic flux appears in the air gap 21 between the pole yfaces 23 and 26, and in the airv gap 55 between the pole faces 48 and 54, At

the predetermined ampere-turns, the pull of the fiux in the gap 21 is not enough to overcome the bias of the arm 5, but the pull of the flux in the gap 55 of the plunger 49 is enough to overcome the bias produced by the spring 52, and the plunger 11e moves forwardly in the chamber 34. As it moves it displaces oil from in front of it, and rearwardly through the bore t, where it impinges upon the valve 6I; thence transversely through the groove S5, into the cavity 5t, and thence through the cylindrical outlet 51, the displaced oil moving into the space 68 rearwardly of the plunger (see Fig. 3, wherein the plunger is shown in a forwardly moved position).

The movement of the plunger is retarded b3 the valve arrangement described above. The pressure of the displaced oil on the valve flange 62 compresses the spring 6l! and moves the conical valve portion 5B into the cylindrical outlet 51, one position of which is shown in Fig, 3, throttling the iiow through the outlet 51. The more rapidly the plunger tends to move the more the flow is throttled, and the result of Which is that the plunger moves forwardly at a retarded timed rate.

As the plunger moves forwardly and shortens the length of the interior air gap 55 between the pole faces 48 and 511 Within the winding, the reluctance of the magnetic iiux path as a whole decreases, and the total flux accordingly increases, and the pull in the gap 21 on the arm 1 increases, and iinally reaches a value at which the arm i is moved agains.J its bias to close the contacts of the contactor as described for Fig. l.

A characteristic curve of pull on the arm 1 is shown at the curve B in Fig. 6, the solid line curve B showing the pull on the arm in the gap 21 for the full stroke of the plunger, with the contacter arm experimentally held in open position.

It will be noted that in Fig. 6 when the plunger has moved approximately to the point c, the pull on the arm 1 is at the point g on the curve B, and that thereafter as the plunger moves the pull begins to rise very rapidly or abruptly to the point h.

This curve B was made 'with a contacter biasload d the same as for the above described prior art contacter, for comparison purposes. It will be noted that the curve B in the rst part of the plunger movement lies farther below the biasload line d than the curve A of the prior art device; but that nevertheless the curve B because of its abrupt upward sweep, crosses the bias-load line; this occurs at i when the plunger has arrived at j.

In practice, after the plunger arrives at j, the contaotor arm 1 moves to closed position, closing the external work gap 21; and the plunger continues to move concurrently therewith; with the joint result that the pull on the arm rises higher than the point h, or to the point Ic, due to the closing of the gap 21.

Thus the plunger has a longer movement for timing purposes with the curve B than with the curve A, and me snai pun .e t@ noia the contacts closed is much greater than that at e for the curve A; both due to the abrupt upward sweep for the curve B.

It will he apparent that if that part o-c of the stroke of the plunger were suiiicient for timing in any given case, then a bias-load as low as the dotted line l could be used and the switch closing load would be made accordingly smaller, and the contactor still more economical, without any re- 8 duction in the high contact closing and holding" pull k.

It is believed that this sudden rise of pull in the latter part of movement of the plunger may be explained as follows. Because the pole piece extends well into the winding 25, practically all of the flux developed by the winding will flow longitudinally through this pole piece and appear at the pole face 26 and in the gap 21. But with a large internal air gap 55, the total ilux is relatively weak and there will be, accordingly, considerable dispersal or fanning out of the flux in the gap 21, and this Weak flux, acting on a large area, produces little pull on the arm 1.

Throughout the major part of the movement of the plunger, increments of plunger movement decrease the internal air gap very little proportionally, so that the total ux increases very little proportionally; and the distribution of the flux remains substantially the same, being distributed thinly or at low density over the pole face 5, and the cross sectional area of the working nux in the gap 21 does not change materially; and the pull in the gap 21 increases very little; and the pull remains weak,

There is however, a critical point in the plunger movement at which two things occur: first, the internal air gap has then become so small that for small increments of plunger movement there is a rapid proportional reduction of the air gap and a rapid proportional increase of total flux and density to higher values; and second, as the flux increases to higher values, it attains the characteristic sometimes called stiffness and the flux in the gap 21 ceases to be anned out but in effect concentrates in the gap 21 and this both further increases its density, and reduces its active area.

rihere is thus a critical point in the movement of the plunger at which the flux in the gap 21 begins to increase rapidly (which rapidly increases its density) and at which the flux pattern in the gap becomes less tanned out which latter not only still further increases the flux density, but also decreases its active area.

As is well known, the pull in a magnetic ah` gap is represented by the cross sectional area of the acting flux multiplied by the square of the flux density. So that this double increase of density in the air gap accompanied by a decrease air gap arca, effects an abrupt or accelerating increase in the pull as shown in the curve B, as the end of the plunger approaches closely to the pole piece 46.

This action is different from that in the said prior Rippl patent, as shown in the pull curve A. In the patent, when the plunger is in the rearward position, and there being no magnetic pole piece ahead of it, and accordingly no interior magnetic air gap, the flux from the end of the plunger bends laterally and ows into and through the magnetic ring 28a, and the flux acting on the arm i6 acts through an annular magnetic gap having the small area of the ring. This makes the pull strong, because of high density in small area. As the plunger 35 moves forwardly it is true that the flux density as a whole increases, 1out when the plunger moves forwardly it enters the ring 28a, and the greater part of the flux no longer bends laterally into the ring but goes straight ahead toward the arm I6, so that the flux then is distributed over a circular air gap of large area. The pull on the arm l5 thus does not increase at an accelerating rate due to the 9 increased flux, because of the concurrently greatly enlarged area of the working gap.

The modification of Fig. 4 is similar to the form of Fig. 2 above described except for features of detail which in some cases may be preferred. In this form, a forward pole piece 69 is fitted into the forward end of a brass or other non-magnetic tube 10. A groove 1I in the pole piece has a wire 12 kof brazing material placed therein before the pole piece is inserted into the tube 10; and the fit at this end of the tube is made leak-proof, by heating the parts (preferably by induction heating) to melt the wire 12 and braze the parts together.

At the rearward end of the tube 18 it is closed by a metal head 13 seated in an annular recess in the end of the tube, and sealed by a ring of solder or brazing material 14. A stud 15 is threaded through the hole T6 in the axial center of the head 13 and upon its inner end the guiding head 61 of the valve abuts, and this constitutes afstop for the plunger 49 at its rearward or biased position. A nut 11 on the stud cooperates with the aforesaid bracket 3l to position the device by drawing a shoulder 30 on the tube 10 into engagement with the frame element 2 as described hereinbefore. This shoulder 98 may be formed on the outside of the tube 18 but I prefer to provide it by a separate tubular sleeve 18 loosely telescoped over the outside of the tube 19, and by providing a shoulder 19 on the pole piece 69 against which the other end of the sleeve abuts, theshoulder 19 overlapping the ends of both the tube 19 and the sleeve 18.

The provision of the threaded stud 15 provides a number of advantages.

In assembling the device, the plunger 49 and its valve structure and the spring 52 are first put into the tube 19. The head 13, and without the stud 15 therein, is then placed in position and sealed by the sealing ring 14. While as stated thisv ring may be made of soldering material, it is preferred to use a wire of brazing material and to heat it to a sufficiently high temperature to melt it. This may conveniently be done by electric induction heating. Because of the high temperature of such heating, the air within the tube 18 would otherwise produce pressure within the tube but because of the threaded opening 19 in the head 13, the pressure within the tube remains at atmospheric pressure,

Oil is now poured into the tube 1i) through the threaded opening 16 sufficient to provide the aforesaid level H16. Then the stud 15 is screwed into the opening, and, having a close fit with the threaded opening 16, is practically oil-leak proof. The device may now be mounted in operative position in the contacter and the contacter operated and the timed delay of its operation observed. The rearward retracted position of the plunger 49 is stopped upon the stud 15 as described; and by turning the stud 15 by means of a screw slot 89 in the outer end thereof, the retracted position of the plunger 49, and accord- 4ingly the length of the air gap 55, may be adjustably changed, and this obviously will effect a change in the length of the time interval required for the plunger 49 to move forwardly to the point at which the arm 1 is moved; and the period of delay of the operation may thereby be adjusted.

By means of this adjustment, a number of such devices, produced at the same time in production, may be caused to all have the same time interval of delay, and any differences in the delay time which might result from slight differences in dimensions, winding ampere turns, etc., may all be eliminated, and a quantity of such devices may all be adjusted to be uniform in operating interval.

After this adjustment has been made, then the threaded opening 16 may be finally and hermetically sealed by a ring 8l of solder or the like applied to seal the stud 15 to the head 13.

Thereafter the stud 15 may be used in connection with the bracket 3|, and a nut 11 screwed onto the stud 15 as shown in Fig. 4 to finally mount the device, with the shoulder 38 drawn tight into engagement with the frame element 2, as described above.

It will be observed that the form of Fig. 4 eliminates a number of machining operations which are necessary in the form of Fig. 2.

In either of the forms of Fig. 2 or 4, the rate at which the plunger 49 moves forwardly, under control ofthe valve structure, will depend upon the response'of the valve to the pressure .of dis.- placed oil upon it and this in turn is determined by the strength of the spring 64. In Figs. Zand 4, this spring is shown as abutting upon the flange 59 of the thimble v58. While this spring can in production be made in quantities of substantially uniform strength, in some cases it may. be de sired to provide an adjustment for vit and this is shown in Fig. 5. A number of thin metal shims BSF-83 are provided and placed between .the spring end and the flange 59, and by selectively varying the number of the shims, the compression and strength of the spring can be adjustably varied. This is done before the end of the tube is permanently peened over at 60.

In Fig. 2 or 4, it will be observed that whenr the winding 25 is Lie-energized and the contactor arm 1 is moved to its biased position, ready for another operation, the magnetic flux in the gap 55 dies out and the spring 52 propels the plunger 49 rearwardly to its original position and displaces the oil fromthe rearward end of the plunger back to the forward end, and the valve is immediately opened by the spring 64 to `full open position which allows the plunger to return immediately without delay.

In Fig. 7 is ,illustrated a modification similar in construction and operation to either of the forms of Fig. 2 or 4 but in which the valvefarrangement isv operated magnetically.

In this form (for which in view `of Figs. 2 and 4 a brief description will now suce) the Valve comprises a stem 84 of magnetic material, slidable in a bore 85 along the axis of the plunger 86 with ample clearance with the bore Wallas at 81. The stem 84 projects forwardly from the forward end of the plunger as shown at 88. The forward end vportion of the bore 85 is enlarged as at89 providing a bore shoulder 99 and the plunger retracting spring 89 loosely surrounds the stem 84 and reacts on this shoulder.

At the rear end of the plunger bore 85 it is lflared out into -a conical valve seat 9|; and beyond the valve seat is an enlarged cavity 92 closed at its outer end by a head 93.

The stem extends into the cavity and has a conical valve portion 94 to function as a Valve, in cooperation Vwith the valve seat 9|; and beyond the valve portion the stem has a flange 95 adjustably screw threaded thereon, and between the flange 95 and the bottom 95 of the cavity-92 is a compression spring 91 the tension of which is adinstable by moving the flange 95. The head 93 has a central perforation 98 therethrough comregular in its movement.

municating with the lcavity 92 through a T-shaped passageway 99 in the stem, when the stem rests on the head 93 as it normally does, or communicating with the cavity directly when the stem end is raised from the head in operati-on as will be described.

In operation, iiux produced in the inner air gap 55 by the winding indicated at 25 as for the other forms, acts on the end 88 of the stem and pulls the stem forwardly against the tension of the spring 9'1, at the same time that flux in the gap 55 pulls the plunger 85 forwardly. The oil in the chamber IDB (indicated at ISE) displaced by forward movement of the plunger, ows rearwardly through the bore 85 and through the conical Valve 9|-94 being variably throttled thereat for the purposes described for the preceding forms.

For any predetermined energizing ampere turns and flux, and corresponding adjustment of the spring 91, the valve will be pulled forwardly to a definite position and will predetermine a rate of movement for the plunger, by throttling the oil fiow to a predetermined rate.

If for any reason the ampere turns should increase (or decrease) for example due to a change of energizing voltage on the winding 25, the valve stem will be pulled magnetically farther forward against increasing tension of the spring 91, (or retracted farther rearwardly by the spring 91) and will thus compensate for the change of ampere turns and maintain the rate of oil flow and rate of plunger movement unchanged.

And if the ampere turns should increase (or decrease) at different times because of a change of temperature and the resulting change of resistance of the winding, a like compensation will be effected.

This form is therefore preferred when constant timing is wanted under circumstances which may cause the ampere turns of the winding to vary. Otherwise the mode of operation and construction is the same as described for the other forms.

In general, as to the several forms, it is preferable for the main tubular chamber wall to be of non-magnetic material in order not to divert any of the magnetic ux out of the working air gap 55. The chamber wall rearwardly of the gap `55 however can be made of magnetic material, and the reluctance of the magnetic circuit as a whole will thereby be decreased with advantages of economy; and that is the purpose of the magnetic rear wall portion 38 of Fig. 2.

Obviously therefore, the entire chamber wall of Fig. 2 could be non-magnetic: or the rear portions of the chamber walls of Figs. 4 and 7 could De magnetic.

In either case, the main part of the uX from the winding and in the plunger 9 ows from the plunger into the return path provided by the frame element 2, following in general the dotted line |01 of Figs. 2, 3, 4, or 7; and there will be some magnetic attraction between the plunger 49 and the frame element 2. When the rear part of the chamber wall is non-magnetic as in Figs. 4 and 7, this attraction is negligible, because of the large gap providedvby the thickness of the non-magnetic wall. But when the rear part of the wall is magnetic (for the advantages noted above) this air gap is very thin, being that only of the sliding nt clearance between the plunger 49 and the wall, and the attraction is accordingly greater and may in some cases cause the plunger to drag frictionally on the wall and make it ir- In such cases therei the tube HEI and disc 03 are unnecessary.

fore it may be desirable to artificially increase this gap, and this may be done as shown in Fig. 3 as a modification, wherein a sleeve of nonmagnetic material |88, is fitted upon and around the plunger, moving therewith. It has been found that a very thin sleeve |08 will serve the desired purposes and that it may be provided by plating non-magnetic metal on the plunger.

In Fig. 4 is shown another modification which may be utilized in all of the described forms. A thin non-magnetic washer |09 is spot welded upon the pole face 48 of the pole piece 59 to prevent magnetic sticking of the end of the plunger i9 on the pole piece after the plunger has engaged it at the end of its stroke.

In Fig. S is illustrated a modification which may be used in place of the above described bracket 3| to hold the timing device rearwardly against its shoulder 3i) for the purposes described. A tube ll is loosely telescoped over the rear end of the timing device and projects beyond its outer end as at |62, The inner end Il of the tube G! extends with ample clearance through a hole HG in the panel and abuts upon the frame element 2. A disc or transverse bar |83 lies on the outer end |02 of the tube IDI. A stud or screw |4 attached to the device as above described projects through a perforation in the disc, and a nut |05 on the stud, when screwed up tight, draws the device rearwardly and engages the shoulder 30 with the frame element 2 and clamps the tube Hl! between the disc |63 and the frame element 2 into a rigid assembly. Means otherwise to support or mount With this arrangement the same parts may be used with different thicknesses of panel 3.

My invention is not limited in all respects to the exact construction, proportion of parts, etc., illustrated and described; and certainly not to its application to an electric contacter, nor to the particular contact-or of the drawing; and my invention is comprehensive or" all changes and modifications which come within the scope of the appended claims.

Iclaim:

l. An article of manufacture formed to be telescoped with an electric winding and to develop a time interval when energized by the winding, comprising: a chamber comprising a tube of non-magnetic material; a magnetic pole piece projecting into and closing the forward end of the tube, and having a flange overlapping the forward end of the tube; a non-magnetic tubular sleeve telescoped over the forward end of the tube and abutting at one end on the flange and at the other end providing an external shoulder on the tube; the tube adapted to be projected into a bore in a support, with the sleeve shoulder engaging the support, and the sleeve formed to be telescoped with an energizing winding between the support and the forward end of the magnetic pole piece; a transverse head closing the rearward end of the tube; a stud screw threaded through the head and projecting forwardly and rearwardly therefrom; a plunger reciprocable in the tube; a spring tending to propel the plunger rearwardly; the pole piece and the forward end of the plunger being spaced apart in the propelled position of the plunger providing an air gap therebetween; a passageway through the plunger; a valve in the rear end portion of the passageway; the plunger being stopped rearwardly upon the stud and the length of the air gap being accordingly determined by the longitudinal position of the stud.

2. In a magnetic timing device, a chamber comprising a tube of non-magnetic material; a magnetic pole piece projecting into and closing the forward end of the tube, and having a flange overlapping the forward end of the tube; a nonmagnetic tubular sleeve telescoped over the forward end of the tube and abutting at one end on the flange and at the other end providing an external shoulder on the tube; a transverse head closing the rearward end of the tube; a stud screw threaded through the head and projecting forwardly and rearwardly therefrom; a plunger reciproca-ble in the tube; a spring tending to propel the plunger rearwardly; the pole piece and the forward end of the plunger being normally spaced apart when the plunger is propelled, providing an air gap therebetween; a passageway through the plunger; a valve in the rear end portion of the passageway; the plunger being stopped rearwardly upon the stud and the length of the air gap being determined by the longitudinal position of the stud; a support through which a rearward portion of the tube extends with the external shoulder abutting on the forward side of the support; a nut on the rearwardly projecting portion of the stud; mounting means clamped between the nut and the rearward side of the support and a winding surrounding the forward portion of the tube forwardly of the support.

3. In an electromagnet structure for operatively moving a biased movable armature load and of the type comprising a magnetic working pole face for confronting the load through a work gap; an energizing winding; means eifective upon energizing the winding to cause magnetic uX and pulling force to develop in the work gap and to increase during a predetermined time interval from values incapable of moving the load, to values which move the load, Iand to cause the increase to go on at substantially one rate during a rst part of the interval and at a rapidly accelerating rate during the latter part of the interval; said means comprising a tubular walled sealed chamber; a stationary magnetic pole piece supported on one end of the chamber and having the said working pole face thereon externally of the chamber, and spaced therefrom and having an inner pole face within the chamber; a rearwardly spring-biased forwardly movable magnetic plunger within the chamber having a plunger pole face normally spaced from the said inner pole face providing an inner magnetic work gap therebetween; the said winding surrounding the inner gap and an inner part of the pole piece; the rest of the pole piece projecting out of the winding and disposing the work gap outside the winding; the plunger being movable forwardly against its bias by the pulling force of flux in the inner gap; the plunger transversely tting within the chamber wall with small clearance, and guided thereby; a passage in the plunger extending from its forward portion to its rearward portion; liquid in the chamber displaced from in front of the plunger and iiowing through the passage upon forward movement of the plunger; and means restricting the flow through the passage to retard the forward movement of the plunger; stop means determining the rearward biased position of the plunger; and adjusting means operable through the wall of the chamber to predetermine the position of the stop means to accordingly predetermine the length of 'the inner air gap and the aforesaid time interv-al.

4. In a magnetic timing device, a chamber comprising a tube -at least an elongated forward portion of which is non-magnetic; a magnetic pole piece projecting into and closing the forward end of the tube, a transverse head closing the rearward end of the tube; a screw threaded through the head and projecting forwardly therefrom and having a step portion; a plunger reciprocable in the tube; a spring tending to propel the plunger rearwardly; the plunger being stopped rearwardly upon the stop portion of the screw; and the space between the pole piece and the forward end of the stopped plunger arranged to function as a magnetic work gap to cause the plunger to move forwardly, when a winding is telescoped with the tube and surrounding the gap and energized; liquid in the chamber; a passageway through the plunger; a liquid flow restricting valve in `the rear end portion of the passageway; and the length of the air gap being adjustably preselectable by rotation of the screw to correspondingly adjust the position of its stop portion.

LLOYD RUSSELL RAN SON.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 946,215 Geissinger Jan. 11, 1910 1,292,003 Miller Jan. 21, 1919 1,579,049 Ainsworth Mar. 30, 1926 1,730,688 Rippl Oct. 8, 1929 1,926,480 Foale Sept. 12, 1933 1,957,877 Young May 8, 1934 2,200,109 Wilckens May 7, 1940 2,324,642 Peterson July 20, 1943 OTHER REFERENCES Magnets, Underhill, pages 45, 61 and 62, pub. 1924 by McGraw-Hill Book Co., Inc., N. Y. C. 

